It would certainly be safe to locate the probe so as to measure the absolute hottest stream that you can find, but I guess what bugs me is that if you do this, you are limting throttle response and possibly derating the engine. ECU's generate fuel rampings based upon EGT and RPM. During acceleration, if the fuel is introduced briskly, the ECU will have to cut the fuel increase rate as the EGT begins to bump up against the programmed maximum. That is why I think a more "average" exhaust stream placement is more indicative of the heat/work that the turbine wheel sees due to it's rotation.

It wouldn't bother me so much if the variation was, say, +/- 25 degrees, but it is more like +/- 150 with even modest repositionings. I've often wondered how it is done on the big turbines. The ideal solution is multiple averaged probes, but that is impractical.